84 SCIENCE IN GRECO-ROMAN ANTIQUITY 



As a result, the observatory of Alexandria was able 

 to undertake a systematically planned series of measure- 

 ments to check the figures furnished by Chaldean 

 astronomy. The customary divisions of the day and 

 night being too inaccurate, the Babylonian division 

 into exact hours, already known by Herodotus (II, 

 109), was adopted, and this, coming into current use, 

 was afterwards accepted by the Romans. The sexa- 

 gesimal division of the circle (degrees, minutes, seconds) 

 was also borrowed from the Babylonians ; but other- 

 wise the Egyptian use of fractions having numerators 

 always equal to 1 was preserved. The foundations 

 of trigonometry were also laid. This is proved by a 

 writing of Aristarchus of Samos (310-250 B.C.) in 

 which, following the example of Eudoxus, he attempts 

 to determine the magnitude of the sun and moon and 

 their distance from the earth. The results obtained 

 are satisfactory for the moon but not for the sun. In 

 this writing Aristarchus keeps to the geocentric hypo- 

 thesis, although, as we have seen, he elsewhere maintains 

 the heliocentric hypothesis taken up by Copernicus 

 many centuries later. The way for this hypothesis had 

 already been prepared by the Pythagoreans and by the 

 opinions held by certain groups of Athenian philoso- 

 phers. It is also possible that Aristarchus was en- 

 couraged in his views by the influence of his master, the 

 physician Strato. In spite of its simplicity, the helio- 

 centric hypothesis was opposed for physical and religious 

 reasons ; for example, the Stoic Cleanthes considered 

 it a blasphemy. Its only defender was Seleucus of 

 Seleucis (about 150 B.C.), who gave at the same time a 

 correct explanation of the ebb and flow of the sea, 

 showing by observations the dependence of these 

 phenomena on the position of the moon. He also 

 affirmed, with Heraclides of Pontus, the infinity of the 



universe. 1 



1 15 Heiberg, Naturwiss., p. 62. 



